Moneyness Conventions

A $100 strike call means something completely different when the stock is at $50 versus $150. A trader comparing options across different underlyings, or the same underlying at different times, cannot use strike price directly — a $100 strike is not a fixed reference point, it's an arbitrary number chosen when the contract was listed. What every trader actually compares is moneyness: how far a strike sits from the current price, in some standard unit.

Comparing hikes by steepness, not by altitude

Two mountain trails can both end at "6,000 feet," but that number alone tells you nothing about how hard the hike is — a trail starting at 5,900 feet is a stroll, one starting at sea level is an ordeal. Hikers compare trails by elevation gain, a relative measure, not by the raw final altitude. Options traders do the same thing: instead of comparing raw strike prices, they compare how far each strike sits from the current spot, expressed as a ratio, a number of standard deviations, or a delta. Two $100 strikes on different stocks are utterly incomparable; two options that are both "10% out-of-the-money" or both "25-delta" are directly comparable, because moneyness strips out the arbitrary starting altitude.

The formulas

Three common moneyness measures, from crudest to most useful:

$$m_{\text{simple}} = \frac{K}{S} \qquad m_{\log} = \ln\!\left(\frac{K}{S}\right) \qquad m_{\text{std}} = \frac{\ln(K/S)}{\sigma\sqrt{T}}$$

In plain English: $m_{\text{simple}}$ is just the strike as a fraction of spot — a $110 strike with spot at $100 gives $1.10$, or "10% out-of-the-money." It's easy but ignores time and volatility entirely, so a 10%-OTM option with 3 days to expiry and one with 3 years to expiry get treated identically even though they're worlds apart in probability of finishing in the money. $m_{\log}$ takes the logarithm, which makes calls and puts symmetric around zero and matches how prices actually move (log-normally, in the Black-Scholes world). $m_{\text{std}}$ goes further and divides by the option's own volatility-scaled standard deviation $\sigma\sqrt{T}$, converting the distance into "how many standard deviations away is this strike" — this is the version that actually behaves consistently across different expiries and different underlyings, and it's closely related to $d_1$ in the Black-Scholes formula. In practice, desks often skip all three and quote strikes directly by delta instead — "the 25-delta put" — because delta already blends distance, time, and volatility into one number that also happens to approximate the probability of finishing in the money.

Worked example 1: comparing two very different options

Option A: stock at $50, strike $55, 30 days to expiry, volatility 40%. Option B: stock at $500, strike $550, 30 days to expiry, volatility 40%. Both are "$5 out of the money times 100," which sounds wildly different, but in log-moneyness terms: $m_{\log,A} = \ln(55/50) = \ln(1.10) = 0.0953$ and $m_{\log,B} = \ln(550/500) = \ln(1.10) = 0.0953$ — identical. Both options are exactly 10% out-of-the-money and, with matching volatility and time, will have essentially the same delta and behave the same way relative to their spot. The raw $5 gap was meaningless; the ratio was everything.

Worked example 2: standardized moneyness with different volatilities

Two 3-month (T = 0.25) options, both struck 10% out-of-the-money in log terms ($m_{\log} = 0.0953$), but Option C has $\sigma = 20\%$ while Option D has $\sigma = 60\%$. Standardized moneyness: $m_{\text{std,C}} = 0.0953 / (0.20 \times \sqrt{0.25}) = 0.0953/0.10 = 0.953$ — just under one standard deviation away. $m_{\text{std,D}} = 0.0953 / (0.60 \times 0.5) = 0.0953/0.30 = 0.318$ — only a third of a standard deviation away. Even though both strikes sit at the identical 10% distance from spot, Option D's much higher volatility means that distance is a much smaller, less remarkable move — it will have a delta far closer to 50% (at-the-money-like behavior) than Option C, despite having the "same" raw moneyness. This is exactly why serious options desks never compare strikes on raw percentage distance alone.

Explore this implied-volatility surface by strike and tenor: notice how "10% out-of-the-money" carves out a completely different-looking slice of the surface depending on the tenor you're looking at — another reason raw percentage moneyness misleads and delta-based moneyness is standard.

What this means in practice

FX and equity options desks quote entire volatility surfaces by delta bucket (10-delta, 25-delta, ATM, 75-delta, 90-delta) rather than by strike, precisely so that a "25-delta risk reversal" means the same relative thing on Monday as it does after the stock has moved 5% by Friday. Strike-based quoting only works within a single fixed instant; delta and standardized moneyness are what make comparisons across time and across underlyings meaningful.